Dual-direction OTDR system for inter-node communications

ABSTRACT

Modules for optical time-domain reflectometry (OTDR) are connected via at least one fiber link of a fiber optic communication network. The modules can perform OTDR operations on the at least one fiber link. In addition, the modules can establish an inter-node communication channel between each other on the at least one fiber link. The channel allows the OTDR modules to synchronize their OTDR operations and to exchange information, such as OTDR traces, between each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/220,202 filed Apr. 1, 2021, which is incorporated herein by referencein its entirety.

BACKGROUND OF THE DISCLOSURE

In standard operations, an optical time-domain reflectometry (OTDR)module performs optical time-domain reflectometry (OTDR) on a fiberunder test. When operated, the OTDR module can check the performance ofnew fiber optics links and can detect problems in existing fiber links.

For example, the OTDR module is connected to an end of a fiber span. TheOTDR module includes software and electronics connected to a transmitterand a receiver. Typically, the transmitter and receiver are connected tothe same fiber using a circulator, for example. The transmitter, whichis a high-power laser transmitter, injects signals (e.g., a series ofoptical pulses) into the fiber under test. From the same end of thefiber, the OTDR module then receives light back-scattered by the fiber(Rayleigh backscatter) or reflected back from various points along thefiber. The back-scattered and reflected light returned to the OTDRmodule through the fiber is then directed to the receiver in the OTDRfor analog and digital processing.

When processed, the scattered or reflected light produces traces thatcan characterize the optical fiber. For example, the traces can indicatesplice losses, can be used to measure fiber lengths, can find faults andtheir locations, and can measure the attenuation of the fiber. Overall,the OTDR traces show the performance of the optical components,including the cable, connectors, and splices, of the fiber link. An OTDRmodule can be embedded in a link or a network to monitor operation andperformance. Such embedded OTDR modules offer single-ended OTDRmeasurement capability.

Improvements to OTDR measurements as well as other aspects offiber-optic communication systems are desirable.

SUMMARY OF THE DISCLOSURE

A method disclosed herein is implemented at a first optical time-domainreflectometry (OTDR) module connected to at least one fiber link of afiber optic communication network. The first OTDR module performs anOTDR operation on the at least one fiber link. When it is not performingthe OTDR operation, the first OTDR module sends a first communication onthe at least one fiber link and receives a response on the at least onefiber link having a second communication. In response to the receipt ofthe second communication, the first OTDR module sends a confirmationcommunication on the at least one fiber link and establishes acommunication channel on the at least one fiber link.

The communication link can be established between the first OTDR moduleand a second OTDR module. A method disclosed is also implemented at thesecond OTDR module connected to at least one fiber link. The second OTDRmodule performs an OTDR operation on the at least one fiber link. Whennot performing the OTDR operation, the second OTDR module receives afirst communication on the at least one fiber link and sends a responseon the at least one fiber link having a second communication of thesecond OTDR module. In response to the sending of the secondcommunication, the second OTDR module receives a resend of the firstcommunication on the at least one fiber link and establishes acommunication channel on the at least one fiber link.

As disclosed herein, an apparatus connected to at least one fiber linkto perform optical time-domain reflectometry (OTDR) includes atransmitter configured to transmit optical signals; a receiverconfigured to receive optical signals; a connection configured to couplethe transmitter and the receiver to the at least one fiber link; and aprocessing unit in operable communication with the transmitter and thereceiver. The processing unit is configured to perform the steps of themethods described above.

The foregoing summary is not intended to summarize each potentialembodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional diagram of a fiber-optic communicationsystem having an arrangement of dual-direction optical time-domainreflectometry (OTDR) modules of the present disclosure for providinginter-node communications over a fiber-optic link.

FIG. 2A illustrates examples of embedded OTDR modules of the presentdisclosure.

FIG. 2B illustrates details of a receiver for an embedded OTDR module ofthe present disclosure.

FIG. 3 illustrates optical communication with the dual-direction OTDRmodules between nodes utilizing two fiber spans, one for each direction,of a fiber optic link.

FIG. 4 illustrates a process for inter-node communications using thedual-direction OTDR modules.

FIG. 5 illustrates a configuration fora receiver in a dual-directionOTDR module of the present disclosure.

FIG. 6 illustrates example layers of an inter-node communication channelaccording to the present disclosure.

FIG. 7A illustrates a fiber-optic communication system having multipledual-direction OTDR modules at each node.

FIG. 7B illustrates a fiber-optic communication system having a shareddual-direction OTDR module and an optical switch at each node.

FIG. 8 illustrates an example of a timing protocol for communicationsbetween switched OTDR modules of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

FIG. 1 illustrates a functional diagram of a fiber-optic communicationsystem 10 over a fiber-optic link 40. One node 20A transmits opticalsignals to another node 20B over the fiber link 40. The fiber link 40may include one or more fiber spans 42 of optical transmission fiber.Fiber spans 42 may be of any appropriate length for signal transmissionin an optical communications network. The link 40 may be part of a fiberring network, mesh network, or any other suitable network.

The nodes 20A-B can include appropriate transmitters, receivers,amplifiers, and other optical or optoelectronic components 21 (onlyschematically indicated in FIG. 1 ). These components 21 can be used totransmit, receive, amplify, and process optical signals over the fiberlink 40. The system 10 can support an appropriate communicationarrangement, such as a wavelength division multiplexing (WDM)arrangement in which multiple communications channels having differentwavelengths of light are used on the fiber link 40. Each optical channelmay be modulated relative to the respective carrier wavelength within anappropriate range. In general, one or more channels may be used withsignals modulated at slower or faster data rates about respectivecarrier wavelengths that are supported.

Network management or control equipment 15 can perform networkmanagement of the system 10. The network management equipment 15 can belocated at the network nodes 20A-B and/or at a remote network managementlocation. Either way, the network management equipment 15 cancommunicate with any of the transmitters, receivers, and other opticalnetwork equipment 21 of the nodes 20A-B using suitable communicationspaths. The communications paths may be based on any suitable optical orelectrical paths. For example, the communications paths (for example,represented by dashed lines) may include service or telemetry channelpaths, may include wired or wireless communications paths, and mayinvolve communications paths formed by slowly modulating the normal datachannels on the fiber link 40 at small modulation depths, etc.

As will be appreciated but not shown here, the fiber link 40 may includevarious optical components, splices, connectors, etc. The fiber link 40may also include various optical network equipment modules, such asadd/drop modules, optical switches, dispersion compensation modules,dynamic filter modules, or any other suitable optical network equipment.

The network management equipment 15 associated with the system 10 canacquire optical time-domain reflectometry traces using OTDR modules30A-B at the nodes 20A-B. These OTDR modules 30A-B can be embedded inthe normal operating fiber span scheme of the system 10. In this way,the control equipment 15 can allow a system operator to remotely connectto the network and remotely log in to equipment anywhere in the networkto observe what the OTDR modules 30A-B are reporting.

During system installation and startup, for example, the networkmanagement equipment 15 can determine a fiber line loss profile of thefiber link 40 to optimize the operation and to identify poorconnectors/splices and the like. System diagnostics can be performed toachieve a number of functions, such as: locating a fiber break;performing in-situ monitoring; and locating and monitoring points in thetransmission line undergoing degradation. The diagnostics can facilitatepreventative maintenance to be scheduled before the issues ordegradation becomes an unexpected fiber link failure.

As shown in FIG. 1 , the communication system 10 uses OTDR modules 30A-Bconnected on both ends of a fiber span 42 in the fiber link 40. TheseOTDR modules 30A-B can be embedded OTDR modules incorporated into thenodes (20A-B) of the fiber-optic communication system 10. Of course, theOTDR modules 30A-B can be independent components capable of integrationinto the system 10.

Each OTDR module 30A-B includes software and electronics 38 connected toa transmitter 32 and a receiver 34. As will be appreciated, suchsoftware and electronics 38 can be implemented in one or more processingunits 39 a and memory storage units 39 b. The transmitter 32 andreceiver 34 are connected via a circulator or coupler 36 to the samefiber span 42. The OTDR modules 30A-B can be used independently, or canbe used in-concert, depending on the application.

During operations, for example, the OTDR modules 30A-B can performstandard Optical Time Domain Reflectometry (OTDR) to monitor attenuationalong the span 42 of the fiber link 40. Additionally, the OTDR modules30A-B can perform Link Continuity Validation (LCV) to determine a validclosed bidirectional optical circuit between the two nodes (20A-B).

To do OTDR monitoring, both of the OTDR modules 30A-B can check theperformance of the fiber optic link 40 and can detect problems in thefiber link 40. For example, a first of the modules 30A uses itshigh-power laser transmitter 32 to inject signals (e.g., a pulse or aseries of optical pulses) into the fiber span 42 under test. From thesame end of the fiber span 42, the same OTDR module 30A then receives atits receiver 34 any light scattered (Rayleigh backscatter) or reflectedback from various points along the fiber span 42. The back-scattered andreflected light returned to the OTDR module 30A is then directed forprocessing to construct a first OTDR trace of the span 42 from thisfirst direction.

Separately, a second of the modules 30B uses its high-power lasertransmitter 32 to inject signals (e.g., a pulse or a series of opticalpulses) into the fiber span 42 under test. From the same end of thefiber span 42, the same OTDR module 30B then receives at its receiver 34any light scattered (Rayleigh backscatter) or reflected back fromvarious points along the fiber span 42. The back-scattered and reflectedlight returned to the OTDR module 30B is then directed for processing toconstruct a first OTDR trace of the span 42 from this first direction.

As can be seen, the scattered or reflected light when processed producesOTDR traces that can characterize the fiber span 40 from bothdirections. The particular details of such OTDR traces are known so theyare not given here. In general, the traces can indicate splice losses,can be used to measure lengths, can find faults, and can measureattenuation in the fiber span. Overall, the OTDR traces show theperformance of components, including the cables, connectors, andsplices, of the link 40.

In addition to performing OTDR and LCV, the OTDR modules 30A-B create adual-direction signal and/or communication channel for communicatingbetween nodes 20A-B. This dual-direction, inter-node communicationchannel is separate from the optical signals (i.e., the wavelengthdivision multiplexing and channels) for which the fiber-opticcommunication system 10 is used. Likewise, this dual-direction,inter-node communication channel is separate from the signals (i.e.,series of optical pulses) used by the OTDR modules 30A-B for OTDRmonitoring. Instead, this dual-direction, inter-node communicationchannel can allow the OTDR modules 30A-B to share their traceinformation with one another and to perform other communicationfunctions, such as described below.

For example, the dynamic ranges of each of the OTDR modules 30A-B can becombined by transferring OTDR information from one node 20A to the othernode 20B and vice versa. This information transfer is accomplishedthrough a Virtual Supervisory Channel (VSC) in a signal processingdomain of the OTDR modules 30A-B. The inter-node communication usingsuch a channel of the OTDR modules 30A-B can be used for a number ofpurposes, as will be appreciated by the benefit of the presentdisclosure.

It will be appreciated by one skilled in the art that any suitable formsof processing unit 39 a and memory unit 39 b can be used for the OTDRmodule 30A-B, and the details of such hardware components would be knownto one skilled in the art. As just one example, the OTDR module 30A-Ccan include a field-programmable gate array integrated intooptoelectronic components 21 of a node 20, which can include atransceiver module, in a fiber-optic network.

Briefly, FIG. 2A illustrates further examples of OTDR modules 30A-B ofthe present disclosure in a fiber-optic communication system 10. Thisimplementation shows the OTDR modules 30A-B embedded at the nodes 20A-B,one at either end of a fiber span 40. Reference to “embedded” for theOTDR modules 30A-B means that the module 30A-B can be put on a line cardin the system 10, as opposed to being a piece of stand-alone Test andMeasurement equipment used temporarily on the link 40 but then removed.

As shown, the OTDR modules 30A-B at the nodes 20A-B are typicallyconnected to the fiber link 40 via a Wavelength Division Multiplexer(WDM) filter 24 or another device to route (switch) signals withwavelength selective switching. The laser in the module's transmitter 32operates at a different optical frequency to the optical frequencies ofthe transmitters (not shown) in the system 10 so the OTDR laser signalscan be multiplexed optically by the WDM filter 24. One OTDR module 30Amonitors the span 40 in the same direction as the WDM signalstransmitted from one node 20A to the other node 20B, while the otherOTDR module 30B monitors the span 40 in the opposite direction.

At the nodes 20A-B, the WDM filters 44 can route OTDR measurementsignals and communication signals to the OTDR module 30 and can routethe WDM signals to other components of the node 20A-B, such as anamplifier 26 or the like. For the OTDR module 30A-B to supportcommunications over the span 40, the receiver 34 of the OTDR module30A-B needs to support different types of inputs, namely one for OTDRmeasurement signals and another for communication signals.

FIG. 2B schematically illustrates a receiver 34 of the OTDR module (30)and additional processing components. For OTDR functions, the receiver34 is configured to support inputs in the form of pulse or coded signalswith high to very low optical power. For communication functions, thereceiver 34 is configured to support inputs in the form of digitalsignals with moderate to low/high optical power.

Therefore, the OTDR receiver 34 preferably employs a lineartrans-impedance amplifier (TIA) 57 with variable gain for bestperformance for the OTDR functions and inputs. In contrast, the OTDRreceiver 34 preferably employs a limiting amplifier 57 for correctdecisions of binary data used in digital communications. To support bothOTDR and communication functions in the OTDR module 30, the receiver 34can use a reverse-biased photodetector 51, followed by alow-capacitance, wideband electrical switch 55 connecting two paths. Onepath from the switch 55 is for linear amplification (G) by the linearamplifier 53 for the OTDR functions, and the other path is for theswitch 55 is for limiting amplification (L) by the limiting amplifier 57for digital communication functions. Both of these paths connect tosoftware and electronics equipment 60 of the OTDR module (30) forfurther processing as disclosed herein.

FIG. 3 illustrates optical communication with the dual-direction OTDRmodules 30A-B in the system 10. An optical switch is used to connecteach OTDR to both fiber spans. Two nodes 20A-B are shown, utilizing twofiber spans 42 a-b, one for each direction. Similar to the system 10 ofFIG. 1 , the OTDR modules 30A-B can perform optical fiber monitoringbetween the nodes 20A-B. As shown in FIG. 3 , the nodes 20 a-b use onefiber span 42 a-b per direction, and the OTDR pulsing is multiplexed toone fiber span 42 a-b at a time.

The OTDR modules 30A-B are used on both nodes 20A-B for fibermonitoring. A multiplexing switch 22 a-b monitors the two fiber spans 42a-b with one OTDR module 30A-B on each of the nodes 20A-B. Informationcan be transferred between the OTDR modules 30A-B from one node 20A tothe other node 20B and vice versa for any suitable purpose. Again, thisinformation transfer is accomplished through a Virtual SupervisoryChannel (VSC) in a signal processing domain of the OTDR modules 30A-B.Details of the inter-node communication using such a channel the OTDRmodules 30A-B are described in more detail below.

FIG. 4 illustrates a process 100 for inter-node communication using thedual-direction OTDR modules 30A-B of the system 10 as in FIG. 3 . Duringoperation, the nodes 20A-B synchronize their fiber scans (Block 102).This can use protocols similar to carrier-sense multipleaccess/collision detect (CSMA/CD) protocols. Once synchronized, thenodes 20A-B alternate the scans between fiber spans 42A-B by using theswitch 22 a-b so simultaneous probing on the same fiber span 42 a-b canbe prevented from both directions (Block 104).

Each node 20A-B decodes its own OTDR trace from its direction (Block106). Using the communication channel (VCS) between the OTDR modules30A-B over the link 40, the nodes 20 a-b exchange their respective datawith the other node 20A-B (Block 108). The process 100 repeats Blocks104 through 108 for the next fiber span 42 a-b (Decision 110) so thatboth fiber spans 42 a-b are traced. The process 100 is entered (andrepeated) during power-up or reset on either side of the communicationlink 40 (Block 112).

Having an understanding of the inter-node communication, further detailsrelated to the signal processing and communication protocols arediscussed below.

FIG. 5 illustrates a configuration for a receiver 50 for use in adual-direction OTDR module (30). The OTDR module's receiver 50 includesan analog front-end on the hardware side followed by a digital receiver60 used for communication processing on the network side 12. The analogfront-end includes a photodiode 51, a trans-impedance amplifier 52, avariable gain amplifier 54, a low pass filter 56, and ananalog-to-digital converter 58. The photodiode 51 detects opticalsignals from the fiber link 40 during operations.

For OTDR processing, the photodiode 51 detects light scattered (Rayleighbackscatter) or reflected back from various points along the fiber inresponse to the signals (e.g., a series of optical pulses) injected intothe fiber link 40 under test from the same node's transmitter (notshown). The OTDR's front-end hardware 50 can process the scattered orreflected light so traces can be produced that characterize the opticalfiber link 40, as noted herein.

For inter-node communication, the photodiode 51 detects lighttransmitted on the link 40 from another node according to thecommunication channel. The OTDR module's receiver 50 receives the lightand uses the analog-to-digital convertor 58 to pass signals to thedigital receiver 60. For handling the channel communications, thedigital receiver 60 includes signal processing 62, data recovery 64, anderror detection/correction 66. For the signal processing 62, softwarefilters are used for enhancing the signal to noise ratio. For datarecovery 64, a demodulator is used and can be based on frequency-shiftkeying (FSK), orthogonal frequency-division multiplexing (OFDM),amplitude-shift keying (ASK), etc. Data slicing can be performed. TheError Detection/Correction 66 can use computations based on Parity,Cyclic Redundancy Checks (CRC), Error Correction Codes (ECC), etc. Thedigital receiver 60 can be implemented in the electronics (38: FIG. 1A)of the OTDR module (30), such as in a digital signal processor (39 a) orin other electronics (21) of the node (20) without additional hardwareneeded. The communication receiver 60 is implemented using signalprocessing in the digital domain.

As noted above, a Virtual Supervisory Channel can be used for inter-nodecommunications between the OTDR modules 30A-B when not operated instandard use for tracing a fiber span. FIG. 6 diagrams a communicationprotocol 70 having some example layers of the Virtual SupervisoryChannel. The communication protocol 70 has a physical layer 72, aprotocol layer 74, and an application layer 76. As will be appreciated,the communication protocol 70 can use more or less such layers dependingon the desired complexity.

The physical layer 72 covers media access (i.e., defines the hardwareand other physical aspects used to send and receive data). The layer 72can employ collision detection with random timeout between the nodes forthe synchronization to be achieved. The physical layer 72 can be basedon suitable modulation, symbol, and data rate, each of which can bechosen by mutual exchange of data streams at various data and symbolrates. For robust communications, the communication channel preferablyuses variables that yield the lowest error rate.

This physical layer 72 interfaces only to the protocol layer 74. For itspart, the protocol layer 74 covers how information is exchanged betweentwo nodes 20 and can include details of the packets, such as header,payload, error detection/correction (CRC/ECC), and the like used. Such aprotocol layer 74 can be responsible for encoding and decoding datapackets to transmit data from node to node and can handle errors,congestion, and packet sequencing. This protocol layer 74 is independentof physical layer 72 and the application layer 76, but interfaces withboth.

The application layer 76 provides interfaces for various applications 78that can use the inter-node communications between the OTDR modules 30of the nodes 20. For example, various applications 78 can use theVirtual Supervisory Channel through socket-like connections.Applications 78 can use the communication protocol 70 to exchange OTDRtraces between the nodes, to exchange status information between thenodes (e.g., node supervisory information), to send control informationbetween the nodes, to downhole code at the nodes, and the like.

As noted previously, the dual-direction OTDR modules 30 may use anoptical switch control. As shown in FIGS. 7A-7B, for example, the OTDRmodules 30A-C may monitor and communicate along multiple fiber spans(e.g. East and West, incoming, and outgoing).

FIG. 7A shows nodes 20A-C having single OTDR modules 30 a-d per span 42a-b of the links 40. For example, each node 20A-C has four OTDR modules30 a-d, one for each span 42 a-d connected to the links 40 to othernodes 20A-C. Communications using the supervisory channel between theOTDR modules 30 a-d are each naturally segregated, which makes thecommunications more straightforward. However, this arrangementduplicates the hardware configurations required at the nodes 20A-C.

In contrast, FIG. 7B shows nodes 20A-C having an OTDR module 30A-Cconnected to a switch 22 for selectively connecting the module 30A-C toa given span 42 a-b of the links 40. As can be seen, the hardwareconfigurations at the nodes 20A-C are simplified, but communicationsusing the supervisory channel between the OTDR modules 30 a-d are notnaturally segregated.

In particular, the OTDR switches 22 at the nodes 20A-C on either side ofa fiber span 42 are not synchronized, so there is no guarantee that theOTDR modules 30A-C on either end of a fiber span 42 will monitor thesame span at the same time. External information, such as from a manualconfiguration can be used to control the synchronization. For successfulcommunication, in the absence of such external information (e.g. frommanual configuration), however, a number of approaches can be used tocommunicate between the asynchronous transmitter/receiver sources.

In a specific embodiment, a timing protocol can be used that ensuresthat OTDR modules 30 on either end of a fiber span 42 are both listeningand transmitting on that fiber span 42. For example, FIG. 8 illustratesa timing protocol 150 for communications between switched OTDR modules30 of the present disclosure. The example timing protocol 150 handlescommunications between switched OTDR modules 30, such as in theconfiguration of FIG. 7B. In the present example, the timing protocol150 is based on a Random Number Generator (RNG), but other timingconfigurations can be used. In general, the timing protocol may berandom or may use some other defined period of time.

As noted previously, a given OTDR module 30 can be used in standardoperation to monitor operation and performance of the fiber spans 42.Likewise, the fiber-optic communication system 10 may be operating instandard operations for fiber optic communication in which opticalsignals are being transmitted along the fiber link 40. If the system 10is operating in standard operations, then it may not be desirable toperform OTDR monitoring with the OTDR modules 30, and/or it may not bedesirable to use inter-node communications with the OTDR modules 30.Accordingly, the protocol 150 may first determine whether the module 30is currently performing an OTDR operation, and/or the protocol 150 mayfirst determine whether the system 10 is operating in standardoperations for fiber-optic communications (Decision 152). If either ofthese cases applies, then using the OTDR modules 30 for inter-nodecommunications may be delayed. If acceptable for a given implementation,however, inter-node communications could be performed at appropriatetimes for the purposes disclosed herein.

When the OTDR module 30 is not in use, a near-end OTDR's receiver 34operates in “Communication Listen” mode to listen for communications(Block 154). The near-end OTDR module 30 defines an order of ports to beprobed (Block 156), and the module 30 uses the switch 22 to switch tothe first defined port (Block 158). Defining the order of ports can berandom using a random number generator (RNG) or can use optimal portselection methods, such as those known and used in the art formulti-connection links.

With the first port selected, the near-end OTDR module 30 uses itstransmitter TX to transmit an initial communication (e.g., an identifier(ID) or the like) of the OTDR module 30 for a defined (e.g., random)period of time (Block 160). The identifier can be any suitablearrangement of pulses set to an established protocol.

After sending the OTDR's identifier, the near-end OTDR module 30 thenlistens for a far-end OTDR's response (e.g., the far-end's identifier(ID)) for a defined (e.g., random) period of time (Block 162). An RNGvalue greater than a minimum can be set to determine that a signal fromthe span communications has been detected (Decision 164).

When a response is received, it may be decoded with processing, and anyverification or lookup steps can be taken. When a response is detectedfrom a far-end OTDR module 30 in that time period, the near-end OTDRmodule 30 transmits a confirmation communication (i.e., retransmits itsOTDR identifier again) in a handshake to the far-end OTDR module 30 andestablishes the inter-node communication channel, defining a repeatingtime period for future communications (Block 166).

If no response is detected at the near-end OTDR module 30, the module 30repeats Blocks 160 through 166 up to a predetermined number N times(Decision 170) at least until a response is detected (Decision 164) andan inter-node communication channel is established (Block 166) or untilanother port needs to be probed (Decision 168). For example, thenear-end OTDR module 30 returns through Blocks 158 to 168 to probe allof the ports of the module 30 connected to fiber links.

If an inter-node communication channel is not established for one ormore ports on the near-end OTDR module 30 (Decision 180), the module 30may return to Block 156, reordering the port order and retrying toestablish the communication channel. In the end, the protocol 150 seeksto establish the communication channel on the ports to the far-endmodule.

Other approaches are possible. For example, a global timing signal canbe used to synchronize control of the optical switches 22 and the nodes30.

In summary of the details disclosed herein, the dual-direction OTDRmodules 30 in the system 10 provide an inter-node communication channelin which the OTDR modules 30 are located at the ends of fiber spans 42.The modules 30 can perform autonomous communications between adjacentnodes 20 at either end of the fiber span 42 without the need for controlvia separate network management equipment 15. As noted, the inter-nodecommunication channel between the OTDR modules 30 can be achieved onmultiple fiber spans 42 using optical switches 22 for time-divisionsharing. The communication channel can be bi-directional for adisaggregated network.

The dual-direction OTDR modules 30 of the system 10 can offer advancedOTDR capabilities that can be achieved by coordinating measurements ateither end of a span 42. For example, the dual-direction OTDR modules 30can provide OTDR traces that have about two times the dynamic rangecompared to just an individual OTDR module. Likewise, the dual-directionOTDR modules 30 can provide an embedded OTDR solution that does notdisrupt live traffic along the fiber span 42.

The dual-direction OTDR modules 30 and their inter-node communicationchannel can be used in a number of applications. In one example, thedual-direction OTDR modules 30 can provide inter-node communications ina disaggregated network. In such a disaggregated network, there may beno centralized network management equipment 15. Instead, each node 20may operate autonomously, and communications are not directly supportedbetween nodes 20 in the disaggregated network. Using the dual-directionOTDR modules 30 of the present disclosure, the OTDR modules 30 on eachend of disaggregated spans 42 can be used to create an inter-nodecommunication channel between the nodes 20 for a number of purposes.

For example, the inter-node communication channel between the modules 30can be used for the setup configuration of the system 10. Usingcommunications between the modules 30 over the inter-node communicationchannel, upstream nodes 20 can inform downstream nodes 20 that they areoptically configured so the downstream nodes 20 can then turn up.

The inter-node communication channel can be used for fault isolation todetect and isolate sections of the system 10 where fiber damage occursbetween nodes 20. The setup configuration and fault isolation can beparticularly useful for high-power Raman systems, where eye safety is ofcritical importance.

The inter-node communication channel can be used for OTDRsynchronization. For example, the OTDR modules 30 on either side of afiber span 42 can be synchronized using communications on the channel toavoid collisions in each other's measurement window.

As one skilled in the art will appreciate with the benefit of thepresent disclosure, the OTDR modules 30 have a number of advancedcapabilities and can communicate/exchange various forms of informationfrom one node to the other and vice versa. At a minimum, the OTDRmodules 30 can communicate/exchange information concerning: (1)operation of the module 30, (2) the OTDR trace conducted by the module30, (3) the setup of the OTDR module 30, (4) a fault on the link, (5)synchronization details to avoid conflicts in a measurement window, and(6) other such information on the established communication channel overthe at least one fiber link from one node to the other and vice versa.

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived of by the Applicants. It will beappreciated with the benefit of the present disclosure that featuresdescribed above in accordance with any embodiment or aspect of thedisclosed subject matter can be utilized, either alone or incombination, with any other described feature, in any other embodimentor aspect of the disclosed subject matter.

In exchange for disclosing the inventive concepts contained herein, theApplicants desire all patent rights afforded by the appended claims.Therefore, it is intended that the appended claims include allmodifications and alterations to the full extent that they come withinthe scope of the following claims or the equivalents thereof.

What is claimed is:
 1. A method implemented at a first opticaltime-domain reflectometry (OTDR) module connected to at least one fiberlink of a fiber optic communication network, the method comprising:sending, from the first OTDR module, a first communication on the atleast one fiber link; receiving, at the first OTDR module, a response onthe at least one fiber link having a second communication associatedwith a second OTDR module; sending, from the first OTDR module, aconfirmation communication on the at least one fiber link in response tothe receipt of the second communication; establishing, with the firstOTDR module, a communication channel on the at least one fiber link withthe second OTDR module; and performing, with the first OTDR module, anOTDR operation on the at least one fiber link, wherein the first OTDRmodule is connected to a plurality of fiber spans of the at least onefiber link, and sending the first communication on the at least onefiber link comprises: defining an order of ports on the first OTDRmodule to be probed, each of the ports connected to one of the fiberspans; and transmitting the first communication on one or more of thefiber spans associated with one or more of the ports selected in thedefined order.
 2. The method of claim 1, wherein the step of sending thefirst communication to establish the communication channel is performedat a time outside of a standard operation for fiber-optic communicationon the at least one fiber link, at a time outside of the OTDR operation,during power-up of the first OTDR module, or during reset of the firstOTDR module.
 3. The method of claim 1, wherein: performing the OTDRoperation comprises synchronizing scans of the at least one fiber linkfor the first OTDR module with the second OTDR module; or performing theOTDR operation comprises: obtaining, at the first OTDR module, an OTDRtrace in a direction of the at least one fiber link; decoding, at thefirst OTDR module, the OTDR trace; and sending, from the first OTDRmodule, the OTDR trace on the established communication channel on theat least one fiber link.
 4. The method of claim 1, wherein transmittingthe first communication further comprises listening for the response atthe selected port for a defined period of time; retransmitting the firstcommunication in response to termination of the defined period of time;and repeating for a predetermined number of times.
 5. The method ofclaim 1, wherein transmitting the first communication further comprises:switching from a previous of the one or more ports to a next of the oneor more ports in the defined order in response to a failure to receivethe response at the previous port; and transmitting the firstcommunication on the fiber span associated with the next port.
 6. Themethod of claim 1, further comprising sending information from the firstOTDR module on the established communication channel to the second OTDRmodule on the at least one fiber link, wherein the information isselected from the group consisting of first data to configure setup ofnodes on the at least one fiber link, second data of a fault betweennodes of the at least one fiber link, third data to synchronize thefirst OTDR module with the second OTDR module on the at least one fiberlink; and an OTDR trace of the at least one fiber link decoded by thefirst OTDR module.
 7. An apparatus connected to at least one fiber link,the apparatus comprising: a transmitter configured to transmit opticalsignals; a receiver configured to receive optical signals; a connectionconfigured to couple the transmitter and the receiver to the at leastone fiber link; and a processing unit in operable communication with thetransmitter and the receiver, the processing unit being configured to:send, from the transmitter, a first communication on the at least onefiber link; receive, at the receiver, a response on the at least onefiber link having a second communication associated with an OTDR module;resend, from the transmitter, the first communication on the at leastone fiber link in response to the receipt of the second communication;establish, with the apparatus, a communication channel on the at leastone fiber link with the OTDR module; and perform, with the apparatus, anoptical time-domain reflectometry (OTDR) operation on the at least onefiber link, wherein the OTDR module is connected to a plurality of fiberspans of the at least one fiber link, and wherein to send, from theapparatus, the first communication on the at least one fiber link to theOTDR module, the processing unit is configured to: define an order ofports on the apparatus to be probed, each of the ports connected to oneof the plurality of fiber spans; and transmit the first communication onone or more of the plurality of fiber spans associated with one or moreof the ports selected in the defined order.
 8. The apparatus of claim 7,wherein the processing unit is configured to send the firstcommunication to establish the communication channel at a time outsideof a standard operation for fiber-optic communication on the at leastone fiber link, at a time outside of the OTDR operation performed by theapparatus, during power-up of the apparatus, or during reset of theapparatus.
 9. The apparatus of claim 7, wherein to perform the OTDRoperation, the processing unit is configured to synchronize scans of theat least one fiber link between the apparatus and the OTDR module; orthe processing unit is configured to: obtain a OTDR trace in a directionof the at least one fiber link; decode the OTDR trace; and send the OTDRtrace on the established communication channel on the at least one fiberlink.
 10. The apparatus of claim 7, wherein to transmit the firstcommunication, the processing unit is further configured to listen forthe response at the selected port for a defined period of time;retransmit the first communication in response to termination of thedefined period of time; and repeat for a predetermined number of times.11. The apparatus of claim 7, wherein to transmit the firstcommunication, the processing unit is configured to: switch from aprevious of the one or more ports to a next of the one or more ports inthe defined order in response to a failure to receive the response atthe previous port; and transmit the first communication on the fiberspan associated with the next port.
 12. The apparatus of claim 7,wherein the processing unit is further configured to send information onthe established communication channel from the apparatus along the atleast one fiber link, wherein the information is selected from the groupconsisting of first data to configure setup of nodes on the at least onefiber link, second data of a fault between nodes of the at least onefiber link, third data to synchronize the apparatus with the OTDR moduleon the at least one fiber link; and an OTDR trace of the at least onefiber link decoded by the apparatus.
 13. A method implemented at a firstoptical time-domain reflectometry (OTDR) module connected to at leastone fiber link, the method comprising: receiving, at the first OTDRmodule, a first communication associated with a second OTDR module onthe at least one fiber link; sending, from the first OTDR module, aresponse on the at least one fiber link having a second communication ofthe first OTDR module; receiving, at the first OTDR module, a resend ofthe first communication on the at least one fiber link in response tothe sending of the second communication; establishing, with the firstOTDR module, a communication channel on the at least one fiber link withthe second OTDR module in response thereto; and performing, with thefirst OTDR module, an OTDR operation on the at least one fiber link,wherein the first OTDR module is connected to a plurality of fiber spansof the at least one fiber link, and sending the first communication onthe at least one fiber link comprises: defining an order of ports on thefirst OTDR module to be probed, each of the ports connected to one ofthe fiber spans; and transmitting the first communication on one or moreof the fiber spans associated with one or more of the ports selected inthe defined order.
 14. The method of claim 13, wherein the step ofreceiving the first communication to establish the communication channelis performed at a time outside of a standard operation for fiber-opticcommunication on the at least one fiber link, at a time outside of theOTDR operation performed by the first OTDR module, during power-up ofthe first OTDR module, or during reset of the first OTDR module.
 15. Themethod of claim 13, wherein performing the OTDR operation comprisessynchronizing scans of the at least one fiber link for the first OTDRmodule with the second OTDR module; or wherein performing the OTDRoperation comprises: obtaining, at the first OTDR module, an OTDR tracein a direction of the at least one fiber link; decoding, at the firstOTDR module, the OTDR trace; and sending, from the first OTDR module,the OTDR trace on the established communication channel on the at leastone fiber link.
 16. The method of claim 13, further comprising sendinginformation on the established communication channel from the first OTDRmodule along the at least one fiber link, wherein the information isselected from the group consisting of first data to configure setup ofnodes on the at least one fiber link, second data of a fault betweennodes of the at least one fiber link, third data to synchronize thefirst OTDR module with the second OTDR module on the at least one fiberlink; and an OTDR trace of the at least one fiber link decoded by thefirst OTDR module.
 17. An apparatus connected to at least one fiberlink, the apparatus comprising: a transmitter configured to transmitoptical signals; a receiver configured to receive optical signals; aconnection configured to couple the transmitter and the receiver to theat least one fiber link; and a processing unit in operable communicationwith the transmitter and the receiver, the processing unit beingconfigured to: receive, at the receiver, a first communicationassociated with an OTDR module on the at least one fiber link; send,from the transmitter, a response on the at least one fiber link having asecond communication of the apparatus; receive, at the receiver, aresend of the first communication on the at least one fiber link inresponse to the sending of the second identifier; establish acommunication channel on the at least one fiber link with the OTDRmodule in response thereto; and perform an optical time-domainreflectometry (OTDR) operation on the at least one fiber link, whereinto send, from the apparatus, the first communication on the at least onefiber link to the OTDR module, the processing unit is configured to:define an order of ports on the apparatus to be probed, each of theports connected to one of the fiber spans; and transmit the firstcommunication on one or more of the fiber spans associated with one ormore of the ports selected in the defined order.
 18. The apparatus ofclaim 17, wherein the processing unit is configured to receive the firstcommunication to establish the communication channel at a time outsideof a standard operation for fiber-optic communication on the at leastone fiber link, at a time outside of the OTDR operation performed by theapparatus, during power-up of the apparatus, or during reset of theapparatus.
 19. The apparatus of claim 17, wherein to perform the OTDRoperation, the processing unit is configured synchronize scans of the atleast one fiber link between the apparatus and the OTDR module; or theprocessing unit is configured: obtain a OTDR trace in a direction of theat least one fiber link; decode the OTDR trace; and send the OTDR traceon the established communication channel on the at least one fiber link.20. The apparatus of claim 17, wherein the processing unit is furtherconfigured to send information on the established communication channelfrom the apparatus along the at least one fiber link, wherein theinformation is selected from the group consisting of first data toconfigure setup of nodes on the at least one fiber link, second data ofa fault between nodes of the at least one fiber link, third data tosynchronize the apparatus with the OTDR modules on the at least onefiber link; and an OTDR trace of the at least one fiber link decoded bythe apparatus.